Cotton and Soybean Insect Update
We now a portion of our cotton crop no longer vulnerable to insects. That is, with lateral squares and blooms difficult to find and medium-sized bolls within a node or two of the top. Most cotton in the state is considerably behind this degree of maturity, however, with a few fields only in the 3rd or 4th week of bloom. These very late fields are only now coming into developmental period of maximum susceptibility to stink bug damage. Cotton fields, if not cut out, should be scouted weekly for stink bug damage to 1-inch diameter bolls until at least the 7th, and possibly the 8th week of bloom. We are still getting calls about cotton fields with internal damage to small bolls in the mid-20 to low 30 percent range. That’s certainly too much damage to ignore, especially with bolls at such a premium this year due to our late crop and missing fruiting positions. For help in diagnosing and responding to possible damage to young bolls, check out the stink bug decision aid web app.
Plant bugs also continue to cause damage in some fields; however the time to be concerned about the shedding of small squares is over. We have too little time remaining for a small square make a harvestable boll.
Cotton aphids appear to be hanging on in some of these late-maturing cotton fields, but no economic infestations have been brought to our attention during the past week.
Our most productive light trap for corn earworms in Gibson in Scotland County peaked at a 3-day total of 268 moths on August 15th, for a 3-day average of just under 90 moths per night. Present numbers are very low at this location and light trap counts elsewhere are also extremely low – with some trap counts only in the single digits or teens. It’ll be interesting to see if our next corn earworm moth flight, perhaps beginning in southern NC about now, is higher that our last generation.
We have some recent reports of this same corn earworm species present at moderate to high levels in soybean fields as podworms in some areas. So far, our samples from untreated fields have been identified as almost all podworms as opposed to the pyrethroid-resistance tobacco budworms. If pyrethroid-resistant budworms are not the culprit, control failures with pyrethroids suggest tolerance or resistance to pyrethroids in some podworm populations. Based on calls, pyrethroid tolerance or resistance appears to be more widespread this year.
Article by Jack Bacheler, NCSU Extension Entomologist